The present disclosure relates to an apparatus and method for matching impedance using Standing Wave Ratio (SWR) information.
In general, various communication devices, such as mobile communication terminals, have antennas through which signals of a predetermined frequency are received and transmitted.
As for the antennas, the impedance thereof needs to be correctly made so as to achieve optimum transmission and reception radiation performance.
Therefore, a related art communication device includes an impedance matching unit using a capacitor, an inductor and the like. The antenna impedance matching is made to an optimum level by controlling the impedance of the impedance matching unit.
The impedance matching of the antenna is made in the state where the antenna is located in a free space, and the impedance matching conditions of the antenna are varied according to changes in surroundings.
Particularly, to use a mobile communication terminal, a user holds a terminal body in his hand and brings a speaker close to a speaker, or uses an earphone while placing the mobile communication terminal in a pocket, a bag or the like.
As a user uses a mobile communication terminal by holding the terminal body in his hand and bringing it close to the ear, or uses it with the body placed in a packet, a bag or the like, the impedance matching conditions of the antenna are varied, thus impairing the transmission and reception radiation performance of the antenna, the impedance of which has matched in a free space.
Therefore, communication devices automatically control antenna impedance when the impedance matching conditions of antennas are changed, such that the antennas achieve optimum transmission and reception radiation performance.
To allow an antenna to maintain its optimum transmission and reception radiation performance, impedance changes of the antenna need to be detected.
To this end, the communication devices include a directional coupler, and detect reflected power and forward power output from the directional coupler.
Also, the impedance of the antenna is matched by changing the impedance of the impedance matching unit according to the magnitude of the detected reflected power and forward power to become a standing wave ratio (SWR).
However, the above impedance matching of the antenna is associated with finding the point where the SWR is at the minimum level within a local area, rather than finding the point within the entire area where the impedance of the antenna can be varied.
Also, there are instances where it is impossible to control the SWR to be equal to or lower than a predetermined value.